1. Field of the Invention
The present invention relates to a method and a circuit for demodulating encoded data of facsimile apparatus, and more specifically to such a method and a circuit which features high speed decoding of incoming facsimile signals which are two-dimensionally encoded by, for example, the modified READ (Relative Element Address Designate) encoding scheme.
2. Description of the Prior Art
In order to speed up document transmission in a facsimile system, two-dimensional encoding methods have been employed. An example of such a two-dimensional encoding method is the modified READ encoding scheme standardized by CCITT (The International Telegraph and Telephone Consultative Committee) for Group 3 facsimile apparatus, in "Telegraph and Telematic Services Terminal Equipment, Recommendations of the S and T series" volume VII-fascicle VII.2, pp. 225-235.
Prior to a detailed discussion of the prior art and present invention, the modified READ encoding scheme will be discussed.
The modified READ coding scheme is a line-by-line encoding system in which the position of each changing pixel on the current encoding line is encoded with respect to the position of a corresponding reference pixel positioned on either the coding line, or the reference line which immediately precedes the coding line. After the coding line has been encoded, it becomes the reference line for the next coding line.